In order to find the value of z, proceed as follow:
By using the Pythagorean theorem for the bigger triangle, you obtain:

Now, if you consider the second bigger triangle:

And in the smaller triangle:

Next, replace the second equation for y^2 into the previous one:

Now, replace the previous expression for x^2 into the first equation for z^2 and simplify:
![\begin{gathered} z^2=13^2-(z^2+7) \\ z^2+z^2=13^2+7 \\ 2z^2=169+7 \\ z^2=(176)/(2) \\ z^2=88 \\ z=\sqrt[]{88}=\sqrt[]{4\cdot22}=2\sqrt[]{22} \end{gathered}](https://img.qammunity.org/2023/formulas/mathematics/high-school/xr9p3dne3s5r7g6vlfvax04oc4cc92tcev.png)
Hence, the value of z is 2√22